1. Field of the Invention
This invention relates generally to brake pad wear sensing devices and methods, and more particularly to a wireless brake condition monitor that monitors the thickness of a disk brake pad and utilizes the thermal energy generated by the brakes to transmit that data to a remote receiver.
2. Brief Description of the Prior Art
Brake systems that are used in various types of vehicles such as automobiles and aircraft typically employ high friction brake pads that are connected to a stationary suspension or frame component so as to prevent rotation of the pads. When a braking force is desired, each pad is moved into engagement with a smooth rotor that is typically in the form of a disk. In a disk brake system, a caliper assembly squeezes the rotor between a pair of pads. The pads are typically made of a composite material and the rotor is typically made of metal. The friction between the non-rotating pads and the rotor provides the braking force. The friction surface of each pad is gradually worn away until the pad is consumed and must be replaced. Replacement of brake pads is a periodic necessity. However, a determination as to when pads are in need of replacement is an inexact science.
Failure to replace brake pads in a timely manner may result in damage to the rotor or other components within the brake system, or injury to the vehicle occupants or others due to brake failure.
There are several patents that disclose various brake wear sensing devices, none of which are powered by heat generated by the friction of the brake pads to wirelessly transmit data to a remote receiver.
White et al, U.S. Pat. No. 5,559,286 discloses a vehicle friction material condition measurement system wherein a sensor which responds to both changes in working length and temperature is embedded in a friction lining to provide a signal indicative of both wear and temperature to an electronic control unit which interprets long term averaged change in the sensor resistance measured when the vehicle is stationary as lining wear and short term changes in sensor resistance as representative of lining temperature.
Kyrtsos, U.S. Pat. No. 5,939,978 discloses a temperature sensing brake lining wear indicator which utilizes a temperature sensor assembly embedded in a brake lining of a drum brake assembly. The temperature sensor assembly includes two temperature sensors with a first temperature sensor located at a first distance X from the wear surface of the brake lining and a second temperature sensor located at a second distance X+d from the wear surface. A timing device measures the time period for the first temperature sensor to reach a first predetermined temperature and measures the time period for the second temperature sensor to reach a second predetermined temperature. The remaining useful thickness of the brake lining is determined based on the ratio of the respective time periods.
Strzelczyk et al, U.S. Pat. No. 6,257,374 discloses a brake pad wear sensing system and method wherein a magnet provides a magnetic field and a Hall effect sensor senses the magnetic field and outputs an electrical signal indicative of the sensed magnetic field that is indicative of pad wear.
Thermoelectric cells that convert thermal energy to electrical power are also known in the art. Typically the thermoelectric cell comprises an electrolyte disposed between two metal electrodes. A temperature differential or gradient is imposed between the electrodes to produce a voltage across the electrodes. An electrical circuit is connected to the electrodes to allow for removal of electrical energy from the cell. Generally, the voltage of the cell is proportional to the temperature difference when the cell is connected across a constant electrical load, so that, even the slightest temperature differential will produce a current. Applicant is not aware of any thermoelectric cells that are used in a braking system to operate sensing devices and transmit data to a remote receiver.
The present invention is distinguished over the prior art in general, and these patents in particular, by a solid-state brake condition monitoring system for a vehicle brake system of the type having a rotor rotatable about an axis and a pad mounted on an extendable metal shoe that frictionally engages the pad with the rotor for creating braking force. The monitoring system includes at least one thermoelectric power converter cell secured on a heat absorbing surface of the brake system for producing electrical power in response to thermal energy, an electronic distance sensing transducer powered by the power converter cell for sensing the distance of the metal shoe relative thereto when extended and outputting an electrical signal corresponding to the sensed distance, the signal being indicative of pad wear, and a signal processing and RF transmitting module coupled with the distance sensing transducer and powered by the power converter cell for receiving the electronic signal from the distance sensing transducer and transmitting a RF signal corresponding to the signal indicative of pad wear to a remote RF receiver.
It is therefore an object of the present invention to provide a wireless brake condition monitor system and method that monitors the thickness of a disk brake pad and utilizes the thermal energy generated by the brakes to transmit that data to a remote receiver
It is another object of this invention to provide a solid-state wireless brake condition monitor that has no moving parts and will last indefinitely with no service required.
Another object of this invention is to provide a wireless brake condition monitor in a miniature package that can be easily secured to a conventional brake caliper.
Another object of this invention is to provide a wireless brake condition monitor that is powered from the heating of the brakes and does not require batteries or connections other sources of power.
A further object of this invention is to provide a wireless brake condition monitor that will provide data representing the condition of the brake pads each time the brakes are applied.
A still further object of this invention is to provide a wireless brake condition monitor that is simple in construction, inexpensive to manufacture, and rugged and reliable in operation.
Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The above noted objects and other objects of the invention are accomplished by a solid-state brake condition monitoring system for a vehicle brake system of the type having a rotor rotatable about an axis and a pad mounted on an extendable metal shoe that frictionally engages the pad with the rotor for creating braking force. The monitoring system includes at least one thermoelectric power converter cell secured on a heat absorbing surface of the brake system for producing electrical power in response to thermal energy, an electronic distance sensing transducer powered by the power converter cell for sensing the distance of the metal shoe relative thereto when extended and outputting an electrical signal corresponding to the sensed distance, the signal being indicative of pad wear, and a signal processing and RF transmitting module coupled with the distance sensing transducer and powered by the power converter cell for receiving the electronic signal from the distance sensing transducer and transmitting a RF signal corresponding to the signal indicative of pad wear to a remote RF receiver.